The present invention relates to devices, such as magnetoresistive (MR) sensors or electronic circuits, having submicron features that are manufactured with a mask that is undercut, with the undercut allowing the mask and overlying materials to be lifted off.
FIG. 1 shows a prior art step in the formation of a conventional MR sensor for a hard disk drive. Over a wafer substrate 20 a magnetic shield layer 22 has been formed, either directly on the substrate or on an intermediate layer, not shown. Atop the shield layer 22 a first read gap layer 24 of dielectric materials has been formed, and atop the read gap layer 24 a plurality of MR sensor layers 26 has been formed. A bi-layer mask 25 has been formed of layers 27 and 28, and after photolithographic patterning, layer 27 has been chemically removed relative to layer 28, forming undercut edges 30 and 33. A directional removal step such as ion beam etching (IBE) has been performed to create edges 35 and 36 of the sensor layers 26, the IBE also removing part of the read gap layer 24.
In FIG. 2 a bias layer 40 has been sputter deposited, followed by an electrically conductive lead layer 44. The electrically conductive bias layer 40 and lead layer 44 abut the edges 35 and 36 of the sensor layers 26 to stabilize magnetic domains of the sensor layers and provide electric current to the sensor layers. The bias layer 40 and lead layer 44 are also deposited atop mask layer 25, but due to undercuts 30 and 33, a chemical etch can be applied that dissolves mask layer 27 allows the mask and the layers 40 and 44 atop the mask to be lifted off.
FIG. 3 shows a cross-sectional view of the sensor layers 26, bias layer 40 and lead layer 44 after the mask has been lifted off. This cross-sectional view of the sensor layers is essentially that which will be seen from a media such as a disk, after the wafer 20 has been diced and the die or head containing the sensor layers 26 has been positioned adjacent the media in a drive system. An active width or track width TW0 of the sensor layers 26 between lead layers 44 may be in a range between one-half micron and one micron, corresponding to a resolution at which the sensor layers can read magnetic tracks in the media.
FIG. 4 is a top view of the sensor layers 26, bias layer 40 and lead layer 44 of FIG. 3. The wafer and thin film layers will, as mentioned above, be diced along the dashed line 3xe2x80x943 that indicates the cross-sectional view of FIG. 3. The sensor layers 26 shown in FIG. 4 have been trimmed along back edges 50 and 52 distal to the dashed line 3xe2x80x943 by conventional masking and IBE such as ion milling, not shown. The leads 44 are typically so much thicker than the sensor layers 26 that the ion milling of the back edges 50 and 52 of the sensor layers 26 does not cut through the leads. The leads have a lead height LH0, measured from the dashed line 3xe2x80x943 that will be the approximate location of the media-facing surface, of about 50-100 microns.
After forming the back edges 50 and 52, another read gap layer, not shown, is formed over the sensor layers 26 and lead layer 44 shown in FIG. 3. A magnetic shield layer that may optionally serve as a write pole layer, not shown, is then formed. After optional formation of a write transducer, not shown, the wafer 20 upon which perhaps a thousand of these sensors has been formed is diced into rows of sensors, one of the rows diced along the dashed line 3xe2x80x943. The structure shown in FIG. 4 is symmetrical about line 3xe2x80x943, so that a pair of sensors may be formed upon cutting along that line 3xe2x80x943, each of the sensors having a media-facing surface adjacent to line 3xe2x80x943. After further processing, including creation of a protective coating on the media-facing surface, the row is divided into individual heads for interaction with a media.
In an effort to increase storage density, the track width TW0 of the sensor layers 26 may be reduced below that current commercially available range of 0.5 micron to 1.0 micron. As the track width TW0 is reduced, however, the undercut used in the lift off process may become a larger fraction of the mask width, so that the lower mask layer 27 can no longer support the upper layer 28. Moreover, reducing the width of mask 25 below 0.5 micron approaches the limits of conventional photolithography.
In accordance with the present invention, methods are disclosed for reducing feature sizes of devices such as electromagnetic sensors. A track width of such a sensor may be defined by a mask having an upper layer with a reduced width and a lower layer with a further reduced width. Instead of or in addition to being supported by the lower layer in the area defining the sensor, the upper layer is supported by the lower layer in areas that do not define the sensor width. In some embodiments the upper layer forms a bridge mask, supported at its ends by the lower layer, and the lower layer is completely removed over an area that will become a sensor. Also advantageous is a mask having more than two layers, with a bottom layer completely removed over the sensor area, and a middle layer undercut relative to a top layer.